Abstract: In order to find out the effect of cotton planting density on fiber quality and yield and determine a reasonable density in the west of Inner Mongolia,it was studied for effects of eight density gradients(120 000,150 000,180 000,210 000,240 000,270 000,300 000,330 000 plants/hm2)of zhongmiansuo50,a early-maturing cotton variety,on cotton fiber quality and yield according through a three-year field experiment at AlashanZuoqi from 2012 to 2014.The results showed that in the cotton planting region of the west of Inner Mongolia;with the increase of planting density of early-maturing cotton,the change tendency of upper half mean length,breaking tenacity,uniformity index,reflectance degree,spinning uniform index were to firstly increase and lately reduce,the change tendency of micronaire and elongation were to drop,the change tendency of yellowness was to rise.But there was no significant difference in fiber quality between different density treatments;within the scope of a certain density,the cotton fiber quality increased with the increase of planting density,but fiber quality began to decline when the density was more than 300 000 plants/hm2;with the increase of planting density,the change tendency of the yield of seed cotton and ginned lint were to firstly increase and lately reduce.The yield of seed cotton and ginned lint were significantly higher than those of other density treatments when the planting density was 240 000~300 000 plants/hm2,and high yield and high quality fiber were achieved the harmonious and unified.The results of this study can provide technical support for the production of high quality cotton in arid area.